I ride a CCM Evox 140 and I picked up one of those speedo computers. Trouble is, the wires are no where near long enough to reach either the front or rear wheel!! Has anyone had any success soldering on extensions to the wires? The wires look to be really fine wire which may not solder too well tho...

If you fit the computer to the clip and run the magnet back and forth past the sensor then you should see some movement on the readout.
To extend the wires it will mean cutting the existing cable at some convenient point and inserting a new section of cable to lengthen it. The wiring cable is a 2 core cable and this will mean 4 joints in total.
You can extend the cable to either reach the front or back wheel.
The wiring is not polarity conscious so it doesn't matter which way round the wires are connected.
When completed make sure the new joints don't short out between wires. Either fit some heat-shrink or insulating tape to the new joints.
The wire carries very little current so use something of similar thickness to the existing one.